AC and Defroster

[LSaupe]

I am considering ordering AC on a new smart and have a few questions if someone could field them.

1. On the operation of the windshield defroster (on those cars equipped with air conditioning). Does the AC pump run while using the winshield defroster (as on many of the newer vehicles to lower the RH exiting the duct)? If so, is there an impact on performance and mileage in the Smart when using the defroster?

2. Has there been any feedback on performance and mileage losses while using AC in general?

Any inputs here are appreciated.

Larry S.

[rollingtones]

Originally Posted by LSaupe

I am considering ordering AC on a new smart and have a few questions if someone could field them.

1. On the operation of the windshield defroster (on those cars equipped with air conditioning). Does the AC pump run while using the winshield defroster (as on many of the newer vehicles to lower the RH exiting the duct)? If so, is there an impact on performance and mileage in the Smart when using the defroster?

2. Has there been any feedback on performance and mileage losses while using AC in general?

Any inputs here are appreciated.

Larry S.

89% of all new cars sold in America have A/C. So you will get better resale value (recovery of some of your costs) at trade-in or resale time.

Yes, the A/C kicks in automatically when you turn the dial to the DEF setting. This helps defrost a windshield. On the smart, as with all other cars, you can have both HOT and DEHUMIDIFIED air at the same time. This is great for drying out wet clothes, etc. Keep in mind that all vehicle A/C systems only run the compressor above about 36 degrees F, so you will not incur any fuel economy penalty below those temperatures due to having the A/C run when you don't deem it necessary.

To save fuel the smart's A/C system uses a time-variable compressor setting. In other words, the more you slide the right-hand temp slider up to a warmer setting, the less often the compressor runs, like with a window A/C unit in a house.

What I do is run the A/C but I usually have the temp selector 1 or 2 clicks down from MAX HOT. This way I get dehumidified, cooler air but it is not like being inside a refrigerator. By the way if you go to MAX HOT you will get exactly that. Just one click down from that gets you cold air.

I am in the car business and I have explained that you can save fuel by varying the temp while still having the A/C on and in 25 years of telling people that, only 3 knew what I was talking about. Another piece of anecdotal evidence to back that up is that every time, without exception, I have gotten into a customer's car in the summer the temp selector was on full cold.

Even using the A/C about 75% of the time since June 1st, I am getting between 40 and 44 MPG on a tank-by-tank average, and I just hit 10,000 miles today, so I drive a lot. I feel that the fuel economy penalty is minimal for the benefits.

[Karl Roth]

agree with rollingtones. Have not seen the severe fuel economy penalty some people are talking about helps clear the windows faster as well.
Good luck with your choice.
karl

[SuperGeek]

I don't see a major hit in MPGs from the A/C, but I can definitely feel the power sapped; I have to turn off the A/C if I feel like I need a power boost. And it adds to the 'power surge' when creeping in traffic at exactly 5mph from the unpredictabilty of when the compressor will kick on. The smart hates to go exactly 5mph; at 4.9 it wants to creep forward... at 5.1 it starts to engine brake and it's evident you've got a manual transmission locked fully in first gear.


The biggest fuel consumption difference is probably at idle; the ScanGauge shows 0.24 gal/hr consumption with A/C off, 0.35 gal/hr with it on and fan selector set to 2 or higher. Oddly enough, setting the fan speed to 1 keeps engine RPMs at 950 and fuel at 0.31 gal/hr. Higher fan speed instantly increases RPMs to 1050. Strange, but maybe it's anticipating more electrical need.

[John_H]

The AC does run when it's 65 degrees, sunny and 5% humidity when you turn the air to not go in your face, not on your feet, and blow the stale air out from the windshield. The AC does automatically turn on when the vents are set to "up" or +/- 1 click from up and there is no mechanism to turn it off.

I have noticed a difference of 3-4 MPG when I had the "up" setting (I don't want "defrost," I want the windshield vents!) during the first few tanks before I knew about the auto-cold setting. The change was immediate with a step function in fuel efficiency from the previous tanks to those that followed.

Once when I mistakenly left the setting too close to up, I did notice the humidity change associated with the A/C turning back off. This is purely anecdotal evidence that the AC might not be on 100% of the time but I can't argue with the results I was seeing.

As for performance - I haven't noticed a big difference with AC on or not. The 71 HP makes this quite the capable little car.

[Woody14619]

I used to have the same issue with my Saturn, which was known for getting fogged. I wound up pulling the relay and fuse for the AC compressor and only putting it in during the few hot months in the summer. I may wind up doing the same thing for the smart if it makes a big difference. The Saturn had a noticeable (7-10 mpg) difference.

And I know... the AC won't come on if its under 35... whatever. Most times when its fogged its because of rain and snow melting. In both cases, it's over 35 when I want to use it! :P

[mvaldes]

Turning a/c on drops my mpg by 3-4 mpg (even with the temp slider set up around 74 - 76) and you do feel the decrease in power. But, you don't have to use it if you don't want to except when you go to clear the windshield. However, when conditions warrant, IMO, being able to see and not wreck the car is worth the few pennies extra in gas burned.

[prm1177]

Originally Posted by mvaldes

Turning a/c on drops my mpg by 3-4 mpg (even with the temp slider set up around 74 - 76) and you do feel the decrease in power. But, you don't have to use it if you don't want to except when you go to clear the windshield. However, when conditions warrant, IMO, being able to see and not wreck the car is worth the few pennies extra in gas burned.

I concur with the economy impact. Running the AC on hot days here in California drops my mileage from a 47-8 mpg average down to 44-5 mpg.

[John_H]

Originally Posted by mvaldes

But, you don't have to use it if you don't want to except when you go to clear the windshield.

If you want the vents directed at the windshield, you have to use the A/C. There's no choice and no indication the AC is on.

If my windows fog, I'd love to hit the A/C button myself!

[saskdiesel]

Originally Posted by John_H

If you want the vents directed at the windshield, you have to use the A/C. There's no choice and no indication the AC is on.

If my windows fog, I'd love to hit the A/C button myself!

Me too.
See this thread.
Disable A/C in defrost?